1. Field of the Invention
The present invention relates to a positioning control device for positioning a head of a disk device in a target position, and a disk device, and more particularly to a positioning control device and so on with which a calculation delay time extending from the acquisition of position information to the output of a control amount can be shortened.
2. Description of the Related Art
With a disk device for a disk such as an optical disk or magnetic disk, it is extremely important to position a head in a target position accurately.
Positioning control is performed by obtaining position information recorded on a medium in the disk device via a demodulation circuit, calculating a control amount for controlling an actuator, outputting the control amount to a drive circuit for driving the actuator, and driving the control subject actuator.
Examples of the prior art relating to this type of positioning control include a device for detecting a defect in servo information (position information) (Japanese Patent Laid-Open H5-62393, for example), a device which, when correct servo data (position information) cannot be extracted, prevents this inability to extract correct servo data from affecting subsequent servo data (Japanese Patent Laid-Open 2000-40318, for example), and so on.
A device for reducing overkill caused by needless write-inhibition also exists (Japanese Patent Laid-Open 2000-163872, for example). In this device, a predicted PES (Position Error Signal) is determined from a value obtained by reading an nth servo pattern, and when the predicted PES satisfies a fixed condition, data writing is prohibited.
Meanwhile, in this type of positioning control, various types of determination processing are performed in addition to calculation of the control amount (Japanese Patent Laid-Open H9-259555, particularly FIG. 2 and so on, and Japanese Patent Laid-Open H10-74371, particularly FIG. 3, for example). An example of a calculation processing procedure including this determination processing is shown in FIG. 17.
First, when a position signal recorded on a medium is acquired, a position error (a distance from a target position to the current position) is calculated. Determination and correction processing is then performed. During this determination and correction processing, the following three main processes are performed.
Firstly, a determination is made as to whether or not the obtained position information is correct, and if not, the position information is corrected. Secondly, a determination is made as to whether or not the calculated current position error is within a suitable range for executing a Read or Write operation. Thirdly, settling determination processing is performed immediately after a seek operation or following deviation from a target track.
Following these determination and correction processes, the control amount of the actuator is calculated, whereupon control calculation post-processing (prediction of the control amount of the following sample) is performed.
FIG. 18 shows an example of a series of processes performed during control calculation in the form of a flowchart. These processes are performed by a control unit in the disk device, for example.
When the processing beings (S100), the control unit calculates the position error (S101) and performs determination processing (S102). When it is determined as a result of the determination processing that the position error needs to be corrected (YES in S103), the control unit corrects the position error (S104), and calculates the control amount using the corrected position error (S105). When correction is not required (NO in S103) the control unit calculates the control amount using the position error calculated in S101 (S105). The calculated control amount is output to the actuator (S106), whereupon control calculation post-processing is performed (S107) The series of processes is then terminated (S108).
The time period from acquisition of the position information to output of the control amount is typically referred to as the calculation delay time. By reducing the calculation delay time, the phase margin can be improved. The phase margin is a reference for evaluating the control characteristics of a control model, and by improving the phase margin, the response speed during positioning control increases, leading to an improvement in control responsiveness. An improvement in the phase margin also leads to an improvement in the positioning accuracy.
Meanwhile, in the calculation processing described above, various determination processes are executed before the control amount is calculated. These processes are extremely important for ensuring the reliability of the obtained position information and position error and so on.
However, when these various determination processes are executed, the calculation delay time from acquisition of the position information to output of the control amount cannot easily be reduced.